The invention relates to a seat belt retractor.
A seat belt retractor for a vehicle has a sensor that responds to changes in vehicle acceleration occurring in a crash. There are usually two sensor inertia mechanisms within the seat belt retractor. The webbing sensor detects payout of the webbing from the seat belt retractor due to the movement of a vehicle occupant when the acceleration of the vehicle decreases or increases. The acceleration sensor comprises an inertia mass either in the form of a ball or a hollow shaped tube acting on a pin or an inertia mass with a relatively high center of gravity located above a narrow base. Movement of the inertia mass acts on a lever positioned in close proximity to the inertia mass to move a toothed portion of the lever into engagement with teeth on a spool or a ratchet thus initiating the locking of the retractor spool and preventing further payout of the webbing.
A typical seat belt retractor, including an acceleration sensor, comprises many cooperating components. One of the problems associated with prior art seat belt retractors is that each component can vary in size due to environmental variations such as changes in temperature during the component manufacturing process. For example, components vary in dimensions when made in multi-cavity tools where more than one component is molded in sequence or at the same time. Also, after large volumes of components have been manufactured in a tool, the molding tool may deteriorate or wear causing variation in component sizes. The variation in sizes creates variability in the relationship between each component. This is particularly undesirable in the acceleration sensor as the spacing between the spool teeth and the acceleration sensor locking teeth requires precision. Variation in the gap between the spool or ratchet teeth and the acceleration sensor locking tooth gives poor repeatability of the acceleration sensor performance. The space between the spool or ratchet teeth and the acceleration sensor locking tooth is called the xe2x80x9ctip gapxe2x80x9d.
If the tip gap is too narrow the acceleration sensor lever may engage with the spool teeth and lock the seat belt retractor in a non-emergency situation. This can create discomfort for the occupant with the seat belt xe2x80x9cjammingxe2x80x9d.
Also, if the various seat belt retractor components have changed in size creating a varying xe2x80x9ctip gapxe2x80x9d, and if the vehicle is positioned at an angle the vehicle occupant may not be able to remove the webbing from the seat belt retractor rendering the seat belt unusable or creating a very sensitive belt which acknowledges and locks the seat belt retractor under non-emergency situations.
It is required that all seat belt retractors lock within specific pay out of webbing under certain vehicle acceleration and declaration conditions. With wide variations in component sizes the seat belt retractor locking times will vary and therefore different amounts of webbing will be released from the seat belt retractor. Such variations result in poor performance and efficiency of the seat belt. The higher the variation in the acceleration sensor performance, the higher the likelihood of experiencing high payout of webbing which will not provide the most effective protection to the vehicle occupant during a crash.
According to a first aspect of the invention there is provided a seat belt retractor comprising a frame, a spool rotatably mounted to the frame, a spool locking device for locking the spool to prevent rotation thereof, actuating means for actuating the spool locking device comprising a support carrying an inertia mass and a pawl, the inertia mass being arranged to move from an initial position to an actuating position to actuate the pawl into engagement with a ratchet on the spool whereby engagement of the pawl with the ratchet actuates the spool locking device, the support being arranged to pivot so as to adjust the distance between the pawl and the ratchet.
In that way the position of the pawl can be adjusted to provide an optimum gap between the pawl tip and the ratchet on the spool.
In one embodiment the pawl is arranged to one side of the support and the support is pivotal about a longitudinal axis thereof.
The support preferably comprises a base having a recess and two end walls upstanding from opposite edges of the base, the inertia mass being received in the recess and the pawl being arranged over the inertia mass, pivotally mounted to an upper part of one end wall.
In such a case the support preferably includes respective pivot members extending from each end wall to enable the support to be pivotally mounted to the frame.
According to a second aspect of the invention there is provided a seat belt retractor comprising a frame, a spool rotatably mounted to the frame, a spool locking device for locking the spool to prevent rotation thereof, actuating means for actuating the spool locking device comprising a support carrying an inertia mass and a pawl, the inertia mass being arranged to move from an initial position to an actuating position to actuate the pawl into engagement with a ratchet on the spool whereby engagement of the pawl with the ratchet actuates the spool locking device, the spool having a cam formation with a circular cam periphery arranged substantially coaxially therewith, the support having a cam follower, the support being mounted movably relative to the spool in response to movement of the cam follower.
In that way the position of the pawl tip relative to the ratchet can continually be adjusted in response to, for example, irregularities in the concentricity of the spool.
Preferably, the support is pivotably mounted to the frame so that movement of the cam follower causes the support to pivot so as to effect automatic tip gap adjustment.
According to a third aspect of the invention, there is provided a seat belt retractor comprising a frame, a spool rotably mounted to the frame, a spool locking device for locking the spool to prevent rotation thereof, actuating means for actuating the spool locking device comprising a support carrying an inertia mass and a pawl, the inertia mass being arranged to move from an initial position to an actuating position to actuate the pawl into engagement with a ratchet on the spool whereby engagement of the pawl with the ratchet actuates the spool locking device,the actuating means comprising a pawl actuating lever pivotally mounted to the support and arranged between the inertia mass and the pawl, the pawl including a cam surface, the pawl actuating lever engaging the cam surface whereby movement of the pawl actuating lever along the cam surface adjusts the distance between the pawl and the ratchet.
In a preferred embodiment of the third aspect, the movement of the pawl actuating lever along the cam surface is effected by means of a movement mechanism comprising a pivot pin which pivotally mounts the pawl actuating lever and a pivot member extending from the pivot pin, parallel with and offset from the axis thereof, and received in the support, whereby rotation of the pivot member effects movement of the pawl actuating lever along the cam surface.
According to a fourth aspect of the invention there is provided a seat belt retractor comprising a frame, a spool rotatably mounted to the frame, a spool locking device for locking the spool to prevent rotation thereof, actuating means for actuating the spool locking device comprising a support carrying an inertia mass and a pawl, the inertia mass being arranged to move from an initial position to an actuating position to actuate the pawl into engagement with a ratchet on the spool whereby engagement of the pawl with the ratchet actuates the spool locking device, the inertia mass engaging the underside of the pawl, the underside of the pawl having a cam surface thereon whereby movement of the inertia mass relative to the pawl along the cam surface effects adjustment of the distance between the pawl and the ratchet.
In a preferred embodiment of the fourth aspect movement of the pawl is effected by a movement mechanism which comprises a pivot pin which pivotally mounts the pawl and a pivot member extending from the pivot pin, parallel with and offset from the axis thereof, and received in the support, whereby rotation of the pivot member effects relative movement of the pawl and inertia mass.